SULFUR ISOTOPE COMPOSITION OF SULFIDES FROM PHOSCORITE AND CARBONATITE OF THE GULI MASSIF (MAIMECHA-KOTUI PROVINCE, RUSSIA): FIRST RESULTS

In order to identify the sequence and conditions of crystallization of sulfides in a carbonatite melt, the isotopic composition of sulfur in pyrrhotite, pyrite, chalcopyrite, jerfisherite, sphalerite, alabandine and valleriite from rocks of the carbonatite series of the Guli alkaline ultramafic massif (Maimecha-Kotui province) was firstly studied using local femtosecond laser ablation and mass spectrometry. Alabandine, manganese-rich wurtzite, and iron-rich sphalerite are successively crystallized in polyphase sulfide assemblages of phoscorite and carbonatite. It was established that wurtzite crystallization began at a temperature of 660 °C and ended at 450 °C. The sulfur isotope composition (δ³⁴S) in sulfide minerals from phoscorite varies from -3.0 to -5.8‰ (n=24), with the exception of two analyses of Ni-bearing pyrite, characterized by a higher δ³⁴S value of -1.6±0.14‰. For sulfides from carbonatite, a steady shift towards lower δ³⁴S values was revealed (δ³⁴S from -3.9 to -6.9 ‰, n=22), which is typical for hydrothermal (carbothermal) environments. The δ³⁴S values for the most common sulfides – pyrrhotite, djerfisherite, pyrite – show variation and decrease from early to late generations, which is explained by an increase in the degree of oxidation and a decrease in the temperature of the carbonatite melt during the successive crystallization of phoscorite and carbonatite. The sulfur isotope composition of sulfides from carbonatite series rocks is indicative of a magmatic fluid source. No values characterizing the transition of sulfur from the sulfide to the sulfate state have been established.